The present invention is generally directed to digital subscriber line (DSL) systems and more particularly to evaluating and troubleshooting DSL systems.
DSL, or xDSL, is a family of technologies that provide digital data transmission over wires of a local telephone network. The two main categories of DSL are Asymmetric Digital Subscriber Line (ADSL) and Symmetric Digital Subscriber Line (SDSL). In ADSL, upload speed is typically lower than download speed. In SDSL, upload and download speeds are typically the same. Two other types of DSL technologies are high speed DSL (HDSL) and very high speed DSL (VDSL).
Several DSL connections, like ADSL and VDSL, typically work by dividing the frequencies used in a single phone line into two primary ‘bands’. Data is carried over a high frequency band (e.g., 25 kHz and above) whereas voice is carried over a lower frequency band (e.g., 4 kHz and below). A DSL filter is typically installed on each phone or inside a network interface device (NID) which connects a customer's inside wiring to the telephone network. This filter typically filters out high frequencies from the phone, so that the phone only sends or receives the lower frequencies (the human voice), creating two independent ‘bands’. As a result, a DSL modem and the phone can simultaneously use the same phone line without interfering with each other.
DSL connections may experience problems. DSL service providers typically detect and troubleshoot DSL service problems by comparing service quality parameters to fixed thresholds. If all crucial parameters exceed their thresholds, the service is believed to be good. Otherwise, an alarm is often issued to denote a service problem. For example, a VDSL system (e.g., line) is required to provide 25 Mb/s bandwidth for “triple-play” (data, voice over IP, and video) service. The bandwidth of the VDSL system is compared to this fixed bandwidth threshold of 25 Mb/s to determine if the VDSL system is operating in an acceptable manner.
Comparing performance parameters to a fixed threshold has several disadvantages. First, if a DSL system is able to perform much better than the chosen threshold but, due to some impairments, it fails to do so, comparing to a fixed threshold will not issue any alarm and the opportunity of providing better service (which is typically more profitable for an ISP) may be missed. For example, a short VDSL line, say 1000 ft, usually can provide 50 Mb/s bandwidth. However, with a bridged tap in the loop, the line can't sustain a rate above 28 Mb/s. Though 28 Mb/s bandwidth exceeds the 25 Mb/s threshold, the line will not be able to qualify for multiple high definition (HD) television (TV) service in the future which usually requires 36 Mb/s. Second, a DSL system slightly above a threshold may still be experiencing one or more problems. For example, a 1 kilofoot DSL line that provides 28 Mb/s (while it should provide 50 Mb/s) is quite possibly encountering excessive ambient noise and/or may have cable issues such as bridged tap. Cable issues and excessive ambient noise often become worse over time. Thus, even if a DSL system meets the threshold today, the DSL system may not meet the threshold a month later. It is usually cost effective to solve a problem earlier rather than later.
It is also typically quite difficult to establish and maintain such a threshold system due to DSL technology evolution. In particular, upgrades in DSL technology result in different thresholds being relevant. Threshold changes may cause confusion as to which threshold is relevant for a given DSL system. The potential for confusion is increased when different DSL speed thresholds are employed for different loop lengths, such as 40 Mb/s for 1 kft lines, 30 Mb/s for 2 kft lines, etc.
As a result, there remains a need for an improved technique to evaluate and troubleshoot DSL systems.